The main reason is the same as vertical tabs - when you have a widescreen, and especially when you have an ultrawidescreen...having it at the bottom just takes up precious vertical screen real estate - moving it to the side has less of an impact on what you can fill your screen with in general. This is more apparent than ever with the Win 11 taskbar given just how thick it is OOTB at least compared to the one in windows 10 - those extra few pixels make all the difference.
Glad you've not seen any bugs yet
I have hit on more today with an explorer crash right clicking on the recycle bin, and some funky notification interactions but nothing major.
I do have more annoyances though mostly on the context menus - it's really not fun constantly going to "show more options" because they decided that we don't need the 3rd party hooks there anymore, resulting in extra clicks to do simple things. Again this is a move targeted at touch, and hopefully there is a config setting to default to the "more" view somewhere...not had time to look for it yet. If anyone finds answers to these things feel free to post them, would be grateful!
Oh, and the date in the taskbar is missing the zero's. So it reads "1/7/21" rather than "01/07/2021" which is a bit irksome (despite my region settings). I have sent some feedback in via feedback hub for all of this though
It's still a nice, if very iterative rather than "next generation", upgrade over 10 in general though!