Apparently it is/was used to enable swap accounting, i.e. it tells the kernel to monitor and restrict swap usage per control groups (cgroups for short). RedHat seems to have started enabling it by default in RHEL7, so apparently the drawbacks are minimal.
You should check your kernel configuration (typically
/boot/config-<kernel_version>). If it includes the line:
then the potential to track swap usage by cgroups exists, and the
swapaccount= boot option is available. Any actual restriction only takes effect if a cgroup with a swap limit is created, and a process is moved into that cgroup.
If it also includes the line:
swapaccount=1 is enabled by default, and you would need to use an explicit
swapaccount=0 boot option to disable it if desired.
systemd and Docker will use cgroups extensively as part of their normal functionality.