You probably have a leak in your roofing material.
If you have a shingled roof, I would judge it to be a nail hole. If you have a roofing membrane, you probably have a crack in a seam.
And yes, you would probably want it fixed right away - water can create an incredible amount of damage in a very short time.
Soft spots on your roof should be addressed immediately as this is an indication that the material under the shingle (outer layer of roofing material) was soaked and is deteriorated to the point of structural instability. Addressing this immediately can significantly limit the amount of additional water damage to the remaining home.
Depending on the age of the home and type of roof framing, there could be a few different causes of a weak spot in your roof. Much of these sources of weak spots are due to old brittle wood or other weak spots inherent in aging wood framing caused by the loss of moisture content in wood from extreme heat degrading the pliability of the wood.
If you have 1x6" roof decking on top of your structural framing, these boards develop weak spots and become brittle over time where there are large knots in the wood or other weak spots that can crack and break easily with foot traffic. If the soft spot is near a roof penetration, either the wood 1x6 plank or plywood sheathing had been cut away too much causing a weak spot. Another cause might be a roof rafter that has a crack in it or some other weakness in the framing member. All of these issues can be inspected from the attic crawl space if access is available.
The need for a repair depends on the severity of the soft spot and type of roofing installed. Some small weak spots like around penetrations are present in many roofs with no leaking issues for the life of the roof. Larger weak spots like those from framing damage, broken roof planks or plywood in the middle of the roof and not around penetrations should be inspected by a licensed roofer or general/framing contractor for integrity of both the roofing substrate and structural integrity of the roof framing.
It means that either the roof decking is rotten and/or the roof rafters are rotten. It does need to be replaced, but it depends on the severity of the damage on how soon it needs to be replaced.
It could be termites or wood rotting. I would get it inspected by a professional to determine what is necessary before it gets worse.