I have some general questions regarding the fix pack upgrades for Websphere Application Server v6.1

1) My environment is running on WAS 6.1 with IHS and PLG for 6.1. When we upgrade it with latest fixpacks. I upgrade WAS and SDK for the AppServers and IHS and PLG fixpacks for IHS and Plugins and i use silent method it upgrade. When i run the GUI method to upgrade for updating IHS and Plugins, the WASSDK fixpack is also picked as available medium to update when i run installation maintenance. Should i be really updating SDK for IHS and Plugins?
Is it Mandatory? I used to do that when i was working for other clients but my present client doesn't never did it and when i did it for the first time everyone asked me why is the reason in doing it? Can anyone help me why is it important to upgrade it. I told them it will update the java in IHS and Plugins. Not sure if i'm right or not?

2) In the past release, fixpack 35 a PM was applied to our WAS6.1 update. Now i'm applying fixpack 37, should i uninstall the PM which is installed with 35 and then install 37 or i can directly install 37 without uninstalling that PM? If we have to uninstall it why should we do that? I thought we don't need to uninstall it as that PM will be covered with the latest release and when updating it with the latest release, WAS will either by pass the update as it is already installed or it will upgrade it if any new items were added to that PM. Not sure if i'm right or not?

I really appreciate for the help.

Thanks in Advance.