If my samples don't have a spike-in, is the CHIP-seq data still going to be reliable?

One of the main purposes of a spike-in is so you can compare global changes in CHIP-seq signal. However, a large amount of researchers who work with ChIP-seq samples don't use a spike-in. If you don't have a spike-in, there are many other metrics you can use to measure the reliability of your ChIP-seq samples such as the alignment rate, the duplication rate, the FRIP score and so forth.