It would depend on what you're using the cat5 cables for. For a POTS line (plain old telephone service), it's fine. For anything like VOIP or data, then no, it's a horrible idea. A network switch would be the appropriate item for connecting several lines to one line.
Splicing a bunch together won't work at all for network devices, but it will work for things like say landline phone lines. But then phone lines don't require cat 5.
Even in a single run, you can't really splice Cat 5 and maintain the rating, you can use cat 5 rated connectors (plugs, jacks, couplers, patch cords, etc.) but even then there are limits in the standards to how many connections you can make between devices. Now with the older 10MBit you get away with murder but with gigabit, or even 100mbit, you don't get away with much. Even older than 10mbit, the old Appletalk would let you run unrated quad (untwisted four conductor low voltage 22 gauge) spliced like phone lines.
Long story short: you want a patch cord between the network device and the jack at the ends, and a single continuous cable between the jacks.
A switch is the most common way to connect multiple network cables (regardless of category rating) to a single point.
Splices / connections, etc before the switch in the single cable is prone to errors / failures.
If you have a large number of cables in one area that are too short, I would install a switch at that location and then install a new cable / cables back to where the main switch is. While not ideal, this may solve your problem and not require you to rerun multiple wires.
If the network was designed this way, this would be likely called an Intermediate Distribution Frame (IDF). This is usually used when your are close to maximum distance for the cable used.
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