Will there be any performance effect if we have more number of Webpart Zones in a Page Layout lets say 25 ? We wont be keeping webparts in all the zones. But we need to have more zones on page layout. So, will be there any performance effect due to adding more webpart zones to a page layout?
Well, strictly speaking, ANY extra processing that the runtime needs to do will have some effect. A more appropriate question would be "will there be a significant effect".
The answer is pretty much "no". Unless you're under massive traffic pressure, you won't notice a difference. No limit on Web Part Zones is specified, however there is a recommended limit for Web Parts of 25, as found here:
The page planning guidelines are here:
But, obviously the complexity of what the Web Parts do is more relevant than the number of Web Parts