the problem with most pour spouts is that they are straight up. While this makes it easier for pouring, it also means that they tend to collect dust far easier, and that is hardly sanitary; the combination of drying liquid and dust is completely unsanitary, making cleaning them something that needs to happen every time they are used.
Pour spout caps are therefore one of the best things available. They cover a pour spout, ensuring that the spout does not collect dust; this minor innovation keeps the spout clean and helps to keep the spout itself nice and clean. While it is still advised to clean off the spout, this does keep them cleaner.
This makes the caps mandatory for those looking to keep their pour spouts clean, especially for those worried about getting sick from them. Caps make your life a little healthier, so make sure you have enough for all your pour spouts.