As we all know, our bodies react to injury by swelling. Surgery is a sterile, organized short term injury to the body in exchange for improvements later on. After an injury, our vessels become leaky and fluid seeps out. Normally, as the original inflammation subsides, the vessels become normal, the leakiness stops and our lymphatics carry such fluid away resulting in tissue softening.
All surgeons have preferences how to drain abdominoplasties and for how long. Some of us are "absolutists" - they either "never" drain or "always remove the drains on post operative day X", while other plastic surgeons are "relativists" - they reserve drains for procedures associated with a lot of fluid creation AND remove such drains when fluid formation falls below THEIR accepted minimally accepted drainage amount. (I happen to fall in the latter group).
In MY opinion, as long as fluid keeps forming in amounts that are superior to the body's ability to take it away, swelling and seromas will form. After being tapped 3-5 times, I think placement of a temporary drain that efficiently removes such fluid is the way to go -- since it keeps the fluid cavity unsder the skin collapsed and more apt to heal while minimizing the hassles of repeated trips to your surgeon's office for fluid tappings.
The known downsides of a persistent fluid collection is formation of a CHRONIC bursa which MAY require a formal operation to correct it and / or infection of the fluid collection.
As regards the hardness of the suture line, unless it is associated with redness or drainage I would not worry about it. It should begin to soften in a few months.
I hope this was helpful.