One of Android’s key strengths is how it handles multitasking. The ability to leave one or more apps running in the background and be able to switch back to them is priceless in a number of use case scenarios. If you have been used to doing this, switching to a budget Android smartphone (in this case, specifically any Android smartphone with RAM of 512 MB or less) can be a little jarring. What you quickly find out is that there is very little multitasking that goes on there, thanks to the low RAM. Usually, when you leave an app and launch another on such a device, chances are that the previous app is shut down at some point. When you return to it, it is opened up all over again.
Multitasking is not quite important to the vast majority of smartphone users. However, it has an impact on the user experience in this case. Low RAM means that you will notice delays in user interaction. It also means that if the app in question requires internet access, e.g. web browser, data is loaded afresh, increasing your data spending.
Of course, as more high end features filter to the budget segment, we can hopefully expect to see more budget Android smartphones with 768MB and 1GB of RAM. After all, years ago, many budget Android smartphones were equipped with only 256MB of RAM. Android OS was launched on the T-mobile G1 in 2008 with just 192MB of RAM. Yes; Android smartphones have come a long way.
If you need a budget Android smartphone and need passable multitasking, if possible, look for one with at least 768MB of RAM. If you cannot, no problems; you still get all the benefits of Android, but just with the above-listed limitations.