Liquid glue is just much neater than tube glue, I use it exclusively. I don't think I've used tube glue in decades. I'm not implying that it's not good or doesn't work but it can be messy, make big blobs or those pesky strings...
liquid glues best feature is that you can assemble the two parts first, holding them together in one hand and then simply touch the fine brush to the seam and the glue is drawn into the seam, (in most cases the entire length of the seam) by capillary action.
They both function the same way in the end since they both melt into the plastic and cause the two parts to weld themselves together. I am currently cleaning up a Finemolds Millennium Falcon that was started by someone else who used tube glue, the parts are melted into each other and have become 'one' in most cases, in the exact same fashion as liquid glue. The difference being the large blobs that surround the small part where it melted into the surrounding area and caused some distortion. Liquid glue evaporates much quicker so this doesn't happen as easily, plus if you're neat/careful you wont get the glue anywhere but inside the seam.
If you are comfortable using tube glue then by all means, keep using it. The benefits to using the liquid glue though can make assembly a much simpler task IMO.
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