Modify User table vs. using JOIN

[Guru]

I've noticed in several hacks that it is common to modify the user table to add fields. This table already has a fairly large number of fields, and adding several hacks that increase this number just makes those queries that much longer.

Another approach is to create a separate table, and use a JOIN SQL query to get the data, yet that seems to be seldom used. Is there a reason that hacks don't add a new table rather than modifying the user table?

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As an example, consider the common hack of making a user contribution table. The hacks here add donate fields. (I'd like to see an amount, a date, and a field indicating whether the user wishes to remain anonymous.) This modification of the user table adds the donate overhead for every user.

The second approach would be to add a new donation table with a few fields. The userid would be the primary key. If only 5% of your users are contributors, your donation table would be much, much smaller. And, the hack wouldn't affect the user table at all. This should be a safer way to hack vB, shouldn't it?

Are there performance considerations, or is it just simpler to add a few fields to the user table?