If resolution is same for different sized monitor then is it wise to go for cheapest?
Is there any benefit to buy 24 inch monitor over 21.5 inch monitor if resolution is same?
In the end both Monitors can show the same amount of information (i.e. the same amount of pixels).
IMHO using a bigger screen instead of a smaller one is just easier on the eyes. But it depends on how fit your eyes are, how far away you are sitting, etc, pp. Just remember: In the end everything (text!) will look a bit smaller on the smaller screen. This can be exausting if you use your screen for long periods of time.
Other factors are (especially for Web Development): * color fidelity * constrast and brightness * Sometimes two monitors of the same model are using different panels with different quality (i'm having this problem with two Acer 22" at work. Same model, different picture!)