This will be a quick one, I've recently found out about this cool possibility within FortiOS. You can select your default wanted Policies Columns displayed within the GUI. This setting is per vDOM though.
In this example, I'm adding the Active Sessions column per policies:
config system settings
set gui-default-policy-columns "name" "policyid" "source" "dstaddr" "schedule" "service" "action" "profile" "logtraffic" "bytes" "active_sessions"
A simple view of the now per default GUI rendering with active sessions:

And you'll find plenty of possible columns to choose from:
fgt (settings) # set gui-default-policy-columns
*name Column name.
name Name.
policyid Policy ID.
srcintf Source.
dstintf Destination.
srcaddr Source Address.
dstaddr Destination.
schedule Schedule.
service Service.
action Action.
logtraffic Log.
poolname NAT.
status Status.
bytes Bytes.
packets Packets.
active_sessions Active Sessions.
last_used Last Used.
first_used First Used.
hit_count Hit Count.
profile Security Profiles.
av-profile AV.
emailfilter-profile Email Filter.
webfilter-profile Web Filter.
application-list Application Control.
ips-sensor IPS.
icap-profile ICAP Profile.
voip-profile VoIP Profile.
profile-protocol-options Proxy Options.
ssl-ssh-profile SSL Inspection.
vpntunnel VPN Tunnel.
comments Comments.
source Source.
users Users.
groups Groups.
gtp-profile GTP Profile.
profile-group Profile Group.
Cheers,
Obuno