Booking roundtrip using different airlines
 

With so many airlines offering one-way fares now, are there any disadvantages of booking this way using different airlines? I'm looking at booking a Jetblue non-stop flight one-way with return flights on Co (Boston-Cancun.)
The fare would be cheaper than booking CO roundtrip, the Jetblue flight is non-stop, and the arrival time back in Boston is much better on CO.
I only fly 3 or 4 times @ yr. so collecting points is not an issue with me.

Only disadvantage would be 2 change fees if your plans change. Also, if your trip is short (e.g., a day trip), and something happens to your outbound flight and you decide to bail on the trip, you may not get any leniency from the return carrier on your change fee. But I'm assuming CUN is not a day trip.

Other than that, it's 2 reservations (and possibly 2 sites to manage), which isn't a big deal.

You're also more likely to get SSSSSed, but only marginally so. And that really isn't too big a deal overall.

I often will book my r/t tix as two one ways when the pricing is the same. There is some loss on the taxes side of things but you get the extra travel club and 500 miles bonus. I copmare the two options and buy the one that gets me a better deal overall.

I've done it several times before without issue. As already mentioned I wouldn't do it on a same day return or late arrival one day and early return the next day but othwise if it makes more sense for your financially, then do it.

Actually for those that do collect miles, some airlines give the same online booking bonus for a one way as they do for a round trip, so if the one way is half of the round trip then you can get your bonus twice booking that way even on the same airline.

Some airlines don't give online bonuses at all for one-way trips (hello, US, can you hear me?).

A problem with buying a r/t is if you change the outbound flight you might have to reprice the whole r/t, thus potentially paying far more for the return.