There are two different ways to join two optical fibers: fiber splice or fiber optical connector. Fiber splices are permanent joints, while fiber optical connectors allow the two fibers to be disconnected at the joint. There are obvious advantages with fiber optical connectors, allowing for changes in network connections or accessing the network for testing. Splices, however, offer lower optical loss at the joint and higher reliability - an advantage for long-distance networks installed outdoors. Sometimes the decision whether to use splices or connectors is made based on less obvious factors.
There are other subtle differences between fiber optical connectors and splices. Take size, for instance. A patch panel of connectors takes up a lot of space, especially when you consider the extra space needed to get a human hand into the patch panel to grab a connector, connect or disconnect it.
Even the so-called “small-form factor” fiber optical connectors take up a lot of space on a panel. The same number of fiber splices will fit in a small, thin splice tray that takes only a fraction of the space required by the same number of connectors.
Splices have less back reflection, an important specification for single-mode networks, especially where high-speed networks are used on short campus or building backbones. But splices may adversely affect the bandwidth of multimode fiber by mode mixing at the splice.
Some fiber splices can be much less expensive if you are doing a lot of fiber joints. This is another big advantage for long distance networks where cables contain many fibers and require splicing every few kilometers. A fusion splice uses a machine to weld fibers together in an electric arc, making the lowest possible loss joint.
Each fusion splice has very low cost, but unless you are splicing many fibers, the extremely high cost of a fusion splicing machine makes fusion splicing unaffordable. Smaller numbers of splices can use mechanical splices, but the individual splices are generally as expensive as fiber optical connectors and take at least as much time to install.