Some people say you should only weigh yourself once per week, and others advocate every morning check-ins. Some argue that weighing every day is obsessive, and can lead to emotional set-back, as your weight WILL fluctuate up and down daily, even hourly. So if you only weigh yourself once per week, you will see the general downward (or upward) trend only.
The other thought is... YES, your weight will fluctuate daily, so if the ONE day you weigh yourself is a "HIGH" day... you may have actually dropped weight, but you'll miss it!
I can see the point for both sides. For me... answer is (like usual)... it depends!
If you are the logical type, like me... I KNOW that my weight will fluctuate up and down all day, as I eat, and as I burn calories. I'm an engineer by education (BS Mechanical/Aeronautical Engineering, Clarkson University, '92), so I'm a born number-cruncher. I'm a charter, a statistics junkie... and frustratingly LOGICAL (to the emotive types in my life). Logical people don't make knee-jerk emotional reactive judgements. So I'm FINE if my weight is not what I expect one morning... because I know what I'm doing WILL work (assuming I'm doing it...), and that in a day or two, my next goal weight will "show up". I know that my body burns 2-3 pounds at night. Typically if I go to bed at 248lbs... I'll wake up at 246. That's how MY body works. How do I know? Because I've tested it. I test everything. Yes, I occasionally weight myself before bed... AND first thing most days! Am I obsessed? No... Am I a logical, number-crunching analytical type who likes to know my status, and understands WHY my weight is changing. It works for my brain... it works for ME. IF I'm tracking my intake, and training like I should... the scale DOES do as I command it. Sometimes it's stubborn... but it MOVES.
If YOU are NOT the LOGICAL type... If you're the type who will starve yourself for a day if the scale reads too high... FIRST... You're hurting you progress, and making things worse! BUT... If you're that person, then daily weighing is NOT for you. In fact some people should NEVER step on a scale. It messes with their brain, then they make desperate changes, and that messes with their body. Those people should find one pair of tight jeans (for the ladies), or a specific belt (for the guys), and use that as their gauge. At MOST they should weigh themselves once per week, typically on Friday, or Saturday morning, right out of the shower, and before their weekend... LOL.
PREFERABLY... People should educate themselves, learn what's going on inside their body, and (attempt to) separate logic from emotion when it comes to the scale, and their fitness level. Fitness (and fat loss with it) are a PROCESS. That process is NOT linear, and that process takes a LOT of time! Trust in that process and your Trainer... and track those damn calories and grams!!!
The scale WILL become your slave, as opposed to the other way around!