Lots of times we travel to a city\place which suffers a lack of a Marriott hotels (any brand). It may not happen in the US, as there's at least one Marriott hotel brand almost everywhere, but it may happen in other parts of the world - in some popular destinations which do not offer a Marriott hotel around. For example: In Europe - Oslo, Norway or Geneva, Switzerland (a 'Moxy' hotel is about to be opened in Oslo in summer 2016).
I was wondering what should I do in such a case... I hate the idea that I'll have to spend my money without getting any perks\benefits along the way, since I'm about to go to Oslo (Norway) soon. After all this time with Marriott, when I've been a platinum member, it does seem to me a waste of money...
So I came into the conclusion that I'd be better having a secondary membership with another hotel chain - a one that is considered to be popular enough and exists in destinations that lack Marriott hotels. My plan is to use this membership as a secondary only, when I don't have any other choice.
My choice as a secondary membership was 'Club Carlson' which includes in its chain the 'Radisson' hotels and a few more.
It was important for me that the secondary club will be able to offer me at least the major benefits which save me money and are offered to me by the Marriott Rewards program:
The first thing I was looking for was a best rate guarantee policy, which I'm personally using for all my bookings. Fortunately, Club Carlson does offer that as well, and with the same conditions as Marriott does (a rate match + 25% reduction). Their advantage regarding this issue is that, comparing to Marriott, they're much less strict with the terms & conditions of how to submit a valid claim form, and using this policy is much easier with them.
The second thing I was looking for was benefits - more or less the same as in my platinum status with Marriott. Fortunately, 'Club Carlson' offer a status match (they will match your Marriott status to their equivalent one). As a Marriott Rewards platinum member I was matched to their gold status. This is not an exact match as their highest status is named 'Concierge', but they never grant it unless you earn it the proper\common way. Luckily, the only significant difference between their gold status and their concierge status is the free breakfast (only concierge status gets breakfast). Gold members are entitled to get complimentary upgrades, bonus points for every stay and even a discount on food & beverages (for a complete list of the benefits see their page).
So now I'm a gold member in their program and used it to book the most central hotel in Oslo they can offer (the Radisson Blu Plaza). Fortunately, all rates in this hotel include breakfast, and I've also managed to reduce my rate by almost 50% using their best rate guarantee policy 
In conclusion, I may be upgraded when I check in and will get points for this stay. I don't know if and when I'll use them but who knows what the future holds? In these cases it's always better to get something than nothing! Obviously, my preference will always be for staying in a Marriott hotel.