Secondary class benefits?

I choose elementalist and am trying to think of possible advantages for choosing a second class, but am having a difficult time thinking of any. On this site, I counted (I believe) 79 elementalist skills alone. This offers a ton of different ways I could play my elementalist at any point.

So, by choosing a second class, do I just throw another 80 some possible skills in the mix? Are there advantages/disadvantages to just sticking to one class? And how far can I go before I will no longer have the option of adding my second class?

There are only advantages to taking a second class, no disadvantages. If you can't decide on which is best for you, just take Monk, because having a resurrect skill is always a good idea. If you missed your chance to take a second profession in Pre-Searing, then there are NPCs out in the EAs of Post-Searing that have quests that can give you a secondary.
If, somewhere down the line, you decide that secondary isn't for you - it will possible to change it later on in the game after you've Ascended. (There are quests that let you switch.)

Advantages for one class:
Not having to spread out your attribute points as much making what you do use more potent.

Advatnage for dual class:
Wider variety of abilities and in some cases to combine your abilities. (for example stacking Necromancers soul barbs with mesmer hexes)

You never have to spread out your attributes. If you play a E/Mo you can still have all your attributes on the E lines. If you then are in a mission where resurect could be useful (most PvE actually), you can bring the monk resurect skill. It will still work even if you have put no attribute point in it. resurected people will be low on hp, so only resurrect them after battle (usually good advice anyway in PvE).

Thats more an exception rather than the rule regarding what you just said about rez. Outside of monk and signets...... point distribution is still a concern.

I don't feel pressed to choose a 2nd class right now though as I'm just learning the Elementalist line of skills. You say that it is possible to change or add a secondary post-searing. Is it something that is really difficult to do or fairly painless? Should I err on taking a second class I don't really like or wait?

I picked up elemental as a second class with my warrior. Haven't seen much written up on this combination, but I like it a lot. Only points I'm investing are in the water line for armor boosting and other effects.

I think that if you do a little research, you can figure out which classes you would like to combine. I suggest picking up your secondary in the pre-searing, even if you don't plan on advancing it at all until later.

Thanks. I will make sure to pick up my second class pre-searing. Though I'll probably stick with mainly elementalist skills for now.