What do you think, is it better for handheld device users to use site menu when its in right sidebar (can click it with thumb/right hand doesnt block view when user click on menu item)? The reason i ask is because a loooot of sites use left side menu and I never understood why, cause IMO its not very comfy nor ergonomic even when using mouse (your mouse is on your right side why should your menu be on left?
Are we talking about mobile specifically? Than the best answer is a dedicated layout.
If it is about desktop browsers than my research indicates that usually right menu helps in giving more relevance to the content (that's why works better for blogs) and left menu works better for apps or shops as gives more emphasis to the navigation itself.
But you really know the right answer, test it with your user group, you might have big surprises!
Web users spend 69% of their time viewing the left half of the page and 30% viewing the right half. A conventional layout is thus more likely to make sites profitable. Horizontal Attention Leans Left
- Sidebars that are mainly navigation should go on the left because it feels more natural to look for navigation there. If you have a lot of navigational links, it might be a good idea to put them in a sidebar.
- Sidebars that are mainly less important things should go on the right, which distracts from the content column less. If you don’t have many navigational links, and you can put them in a horizontal navigation bar near the top, you’ll probably want to go with this option. Right vs. Left Sidebar
Much of this design lies around the English language convention of reading top-to-bottom and left-to-right. It's why you also see many menus at the tops of pages, rather than the bottom. As @igor's answer references, for non-mobile designs, this is convention for a reason.
As for mobile website and applications, there have been quite a few redesigns to focus on the more thumb-accessible portions of the screen. Winamp for Android, for example, places all of its controls at the bottom of the application, with a swipe-up to get at your playlist, etc.
Consider hiding your menu behind a button or swipe action, but if you do, make sure it is easily accessible.
Not a direct answer I guess, but I think the sidebar for navigation in and of itself is often a poor idea for navigation on mobile if scrolling is involved. Mobile phones are portraits whereas desktops are landscapes; a sidebar drastically cuts into extremely limited screen real estate on a mobile phone. horizontal menus at the top tend to take up much less screen real estate and disappear once you scroll down; helpful if there is only reason to navigate once you've opened or finished a page (as with news articles). And often either side is harder to tap than the bottom; where your thumb probably is, regardless of whether you're a lefty or a righty.
As others have said the left hand sidebar is a convention from desktop PCs where it works quite well, however on mobile devices it's not necessarily the case; on a mobile device "sides" of the screen matter a lot less when screen is 2 inches wide and therefor always in focus. On a desktop there's lots of whitespace and lots of panning around the page to find elements, on a mobile display they're often all in view.
The PC style is sidebars on the left, because on a screen, that is the place you start looking. Having established that as the norm, people expect that, and changing it is only done at your peril.
However, mobile phone interactions do not yet have the same sort of conventions. So developing new conventions is valid - if you can design a site with its own conventions and get it working, then try it. But without any existing conventions you are exploring and defining - you need to produce a dedicated layout, but also be prepared that it doesn't work.
Bear in mind that the reading conventions will be different on a phone, so trialing out would be really worth while.