GPS only vs GPS/GLONASS dual antenna for RTK

Will there be a big difference when using RTK with a dual GPS/GLONASS antenna compared to a GPS-only antenna? My experience with GLONASS is limited to my Samsung Galaxy S3 mini (GT-I8190) smartphone being able to get a fix to a very limited number of GLONASS satellites (I may have 7-8 GPS satellites fixed but only 1-2 GLONASS fixes at the same time)… So my question is - is it worth investing into a dual antenna for RTK? I can understand an external antenna is very different situation than using a smartphone, but I am just curious.

Edit: I see the NEO-6T USB dongle is GPS only anyways, so I will probably go with GPS-only antenna at first to save some money. I will appreciate any info on the topic still anyways :).

GLONASS satellites may help sometimes. But as NEO-6T only supports GPS, the only reason for GPS\GLONASS antenna would be for the future use with other GPS\GLONASS receiver.